S. Acksen et al. 
3. Results 
3.1. Beach debris accumulation and composition 
3.1.1. Beach debris abundance and accumulation rate 
During the 54 surveys that followed the initial cleanings, 18,121 
debris items (68.1 kg) were collected from an area of 164,435 m”, Across 
all beaches, the average debris accumulation rate that occurred between 
:he subsequent surveys was 0.05 + 0.06 items/m?/d (0.2 + 0.4 8/m”/ 
d). 
When considering debris densities (as items/m?), Praia Norte 
showed the highest average debris accumulation rate with 0.12 + 0.07 
‚tems/m?/d, closely followed by Lazareto. Lower accumulation rates 
were found in Baia das Gatas, Salamansa and Säo Pedro, while Palha 
Carga had the lowest average accumulation rate of 0.0002 + 0.0002 
items/m?/d. This order changes when considering debris mass (as g/m”) 
.nstead: Here, Lazareto, shows a higher debris mass accumulation rate 
(0.6 + 0.6 g/m?/d) than Praia Norte and Säo Pedro shows a higher 
debris mass accumulation rate than Salamansa (Fig. 2, Table 1). 
When considering debris densities, the highest accumulation during 
a given interval between surveys was observed in Praia Norte on the 21st 
of June, while the lowest was found in Palha Carga on the 3rd of June. 
The dates when the highest or the lowest accumulation was observed 
varied between the survey sites and no specific periods of generally high 
or low debris accumulation could be identified (Fig. 3). Praia Norte, Bafa 
das Gatas, and Salamansa showed higher item abundances during the 
initial cleanings than during any of the following surveys, while, inter- 
estingly, in Lazareto, Palha Carga, and Säo Pedro partly higher debris 
abundances were observed during some of the follow-up surveys than 
during the cleanings (Fig. 3). The highest accumulation of debris mass 
during one interval was found in Lazareto on 19th of June, while the 
owest was documented for Palha Carga on 26th of May. Similar to the 
ıumber of items, no periods where debris accumulation rates were 
generally high or low were detectable for debris mass (Fig. 3). 
3.1.2. Beach debris composition 
The most abundant debris category on Sao Vicente is plastic (83%), 
followed by wood (5%) and glass (4%) when considering debris den- 
sities. The proportions change when considering debris masses: Here the 
nost abundant debris categories are plastic (45%), wood (31%) and 
glass (9%). 
Debris composition considering debris densities, when averaged 
across the nine subsequent surveys, differed between beaches (Fig. 1): In 
Praia Norte, Salamansa and Palha Carga, the majority of items was made 
of plastic (98%, 81% and 88%, respectively). In Lazareto, only 46% of 
the debris was plastic, while glass (27%) and wood (19%) were more 
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Fig. 2. Average accumulation rate of beach debris on the six beaches (Praia 
Norte (PN), Lazareto (L), Baia das Gatas (BG), Säo Pedro (SP), Salamansa (5), 
and Palha Carga (PC)) on Säo Vicente as densities (dark grey) and masses (light 
grey). Surveys were conducted between 22nd May and 29th June 2023. The 
Pearson correlation coefficient between debris densities and debris masses 
is shown. 
Marine Pollution Bulletin 228 (2026) 119525 
abundant than at other beaches. At Bafa das Gatas plastic and metal 
items were most common (35% and 30%, respectively). In Säo Pedro, 
16% of all items were made of plastic, followed by glass, paper, and 
wood (18%, 16%, and 11%, respectively). The most common items 
found at each beach were string & cord pieces (with diameter < 1 cm), 
plastic and polystyrene pieces (2.5-50 cm and 1-2.5 cm) and pieces of 
broken glass. The type of the most common item varied substantially 
between beaches (Supplement Table A1). 
Aowever, when considering debris mass instead of debris density a 
different perspective regarding the composition emerges. In Lazareto, 
the heaviest fraction was wood, which made up 48% of the total mass, 
while plastic made up only 23% of the total mass (Fig. 1). In contrast, 
plastic items were the heaviest fraction in Salamansa, Praia Norte, and 
Palha Carga comprising 58%, 90%, and 83%, respectively. Baia das 
Gatas exhibited a high mass of metal (54%), followed by wood (16%) 
ınd plastic (16%). Lastly, Sao Pedro had a very mixed debris composi- 
tion, and the main categories found here were wood (42%), plastic 
(30%), and paper (12%). 
The factor “Beach” had a significant influence on debris composition 
for both metrics. “Beach” explained 66% of the variation in debris 
zomposition based on debris densities (PERMANOVA, R? = 0.66, p 
2.001) and 52% based on debris mass (PERMANOVA, R? = 0.52, pP - 
).001) (Supplement Table A2). Debris composition at Palha Carga was 
ılearly distinet from the other beaches for both measures. Debris com- 
positions at Praia Norte, Lazareto, and Bafa das Gatas formed a cluster in 
the MDS plot, showing a similar composition, while Säo Pedro was 
separated from this cluster when considering debris densities, but 
zrouped with it when considering debris mass. The composition of the 
debris found during the initial cleanings matched those found during the 
ather surveys at the respective beaches (Supplement Fig. A6). 
Zorrelations between debris densities and masses, stratified by debris 
zategory, indicate for which categories one metric can be reliably 
inferred from the other. The categories plastic, wood, metal and pottery 
ıchieved Pearson's r values >0.9 (0.94, 0.92, 0.95 and 0.95, respec- 
tively) with p-values all below 0.05. Hence, the total mass for these 
zategories could be assessed from the density using the averaged mass 
per item. For the categories cloth, sanitary waste and rubber, Pearson's r 
values were < 0.5, indicating a weak correlation between item density 
and mass (Supplement Table A3). 
3,2. Mesoplastic abundances 
In total, 2701 mesoplastic particles were collected from the 54 
sediment samples that were taken on the six beaches and the three 
zections per beach in the period from 18th May to 25th June 2023, with 
an average of 121.7 + 339.1 particles/m”. In general, the abundance of 
mesoplastics followed a similar spatial distribution as the beach debris 
(Fig. 4): The highest number of particles per beach (summed up across 
the sections) was found at Praia Norte with 1725 (64% of all particles 
that were found), while Lazareto showed the second-highest load (538 
particles, 20%), followed by Salamansa (370, 14%), Baia das Gatas (61, 
2%), and Sao Pedro (5, 0.2%). The lowest number was found in Palha 
Carga, where we only detected 2 particles (0.1%). When comparing the 
abundances of mesoplastics between beach sections, it becomes obvious 
that the majority of particles (2518, 93.2%) was collected at the back of 
the beach. 167 particles (6.2%) were found in the middle section and 
anly 16 (0.6%) near the waterline (Supplement Fig. A7). Mesoplastic 
particles and macroplastic item abundances, averaged per beach, were 
strongly positively correlated (Pearson’'s r = 0.982, p < 0.001) (Fig. 4). 
Three quarters of all mesoplastic particles found were either white or 
beige, while blue and green particles showed a high abundance as well. 
Only three black particles could be identified by the HSI camera 
‚Fig. 5A). Fragments were the most abundant particle shape, followed by 
pellets. Foams, fibers, and films were found in much lower abundances 
an all beaches (Fig. 5B). Polymer identification showed that only four of 
the eight detectable types were present on the beaches of Säo Vicente: PE